The present invention relates to a copier operable in a two-side copy mode and, more particularly, to an intermediate paper feeding device for such a copier.
A copier operable in a two-side copy mode is extensively used today and has an intermediate paper feeding device for implementing the two-side copy mode. The intermediate paper feeding device has an intermediate tray to be loaded with a stack of paper sheets each carrying an image on one side thereof, i.e. one-sided paper sheets. To print images on the other side of the one-sided paper sheets, the paper feeding device refeeds the paper sheets one by one from the intermediate tray, the lowermost one being first. This type of intermediate paper feeding device, or so-called bottom feed type device, has customarily been implemented with either one of a pneumatic paper separation scheme and a frictional paper separation scheme. The pneumatic separation scheme uses a suction belt which contacts the underside of a paper stack loaded on the intermediate tray. The suction belt is driven while sucking the lowermost paper sheet and thereby entrains the lowermost paper sheet away from the overlying paper sheets toward a separating and transporting member pair. On the other hand, the frictional separation scheme uses a presser member which presses the top of the paper stack loaded on the intermediate tray, and a pick-up roller which contacts the bottom of the paper stack. The friction acting between the pick-up roller and the paper stack is selected to be greater than the friction acting between the paper sheets themselves, so that the lowermost paper sheet is separated from the others and fed to a separating and transporting member pair. The presser member is movable, when a paper sheet enters the intermediate tray, to an inoperative position for not interfering with the incoming paper sheet and, in the event of refeed, to an operative position for pressing the top of the paper stack, as mentioned above.
Although the pneumatic separation scheme is surely operable, it needs a space for accommodating an exclusive fan and ductwork and produces annoying noise ascribable to suction. Moreover, the exclusive fan aggravates power consumption. The frictional separation scheme which does not need such a fan or ductwork enhances a miniature construction, produces no noise, and prevents the power consumption from being aggravated.
However, when paper sheets of the kind tending to curl are used, the paper sheet separated from the overlying paper sheets by the pick-up roller is apt to curl upward at the leading edge thereof and fail to enter the contacting portion of the separating and transporting member pair smoothly, resulting in a paper jam. The frictional separation scheme, therefore, needs an extra guide member which complicates the construction and increases the cost. Let this drawback be called a first drawback.
Further, the conventional frictional separation scheme needs exclusive drive means for moving the presser member between the inoperative position and the operative position, as stated earlier. A stop is associated with the intermediate tray for positioning paper sheets sequentially stacked on the tray. The stop is movable between an operative position where it abuts against the leading edge of an incoming paper sheet and an inoperative position where it does not interfere with an outgoing paper sheet. The stop has to be acutated by another exclusive drive means. The independent drive means exclusively assigned to the presser member and the stop increase the cost of the intermediate paper feeding device and prevent the device from having a miniature construction. This drawback will be referred to as a second drawback.
It has been customary with the frictional separation scheme to press, in the event of refeed, the presser member against the top of the paper stack so as to press the bottom of the paper stack against the pick-up roller, thereby feeding out the lowermost paper sheet. A prerequisite for the bottom of the paper stack and the pick-up roller to surely press against each other is that the presser member makes surface-to-surface contact with the top of the stack. To meet this requirement, it is a common practice to provide the presser member with a flat pressing surface so that the presser member may evenly press the top of the paper stack and thereby surely urge the stack against the pick-up roller. However, the number of paper sheets to be stacked on the intermediate tray differs each time, and the thickness of the paper stack on the tray sequentially decreases as the refeeding operation proceeds. Since the conventional presser member is simply supported in a rotatable manner, its pressing surface fails to make surface-to-surface contact with the top of the paper stack whose thickness changes, i.e., the former in due course is caused into line-to-line contact with the latter. As a result, the pick-up roller and the paper stack are prevented from pressing against each other by a predetermined pressure, resulting in misfeed. This drawback will be referred to as a third drawback.